Kang Kek Ieu, who is better known under his revolutionary name, Duch, headed the Khmer Rouge's secret police and ran Phnom Penh's notorious Security Prison S21 in which more than 12,000 people were interrogated and tortured before being killed.

Duch's picture is on display amongst those of the centre's victims

The court's investigating judge, General Ngin Sam An, told reporters that Duch had been charged under two separate laws but, he said, the case was still under investigation and the charges could be amended at a later date.

Duch, who says he has since become a born-again Christian, was located by reporters from the Hong Kong-based Far Eastern Economic Review last month after two decades of hiding.

He admitted his role in the killings to the reporters and said he had personally killed many prisoners. He also implicated other former Khmer Rouge leaders, saying he was prepared to testify against them.

He singled out Khmer Rouge Number Two, Nuon Chea, as having ordered the killings at Tuol Sleng. Nuon Chua is currently living freely in western Cambodia after agreeing immunity terms for his defection with the government.

Safety fears

Duch was taken into custody last Sunday by Cambodian police after human rights groups raised concerns about his safety, and fears that surviving Khmer Rouge members may attempt to silence him.

He has now been charged with murder and torture under a decree passed in 1980. The investigating judge said this was because Cambodia - where some 1.2 million people are believed to have been killed at the hands of the Khmer Rouge - has no law on genocide.

But some legal experts have questioned the validity of the decree, which includes the death penalty for most serious cases , as Cambodia's constitution outlaws capital punishment.

'Butcher' on trial

Ta Mok, "the Butcher", was arrested in March

Duch is now the second Khmer Rouge leader to be prosecuted by the government.

Military chief Ta Mok, known as "the Butcher" is currently awaiting trial charged under a 1994 law banning the Khmer Rouge.

The testimony of Duch, the only member of the group to admit his role in the killings, could prove vital.

Phnom Penh resident Koy Sary, 44, whose brother was tortured and killed at S21, also known as Tuol Sleng, said he was happy to hear that Duch had been charged.

"My brother's picture still hangs on the wall of Tuol Sleng, " he said. "Our anger cannot disappear so easily.